How to Control Fire: Keeping Fire from Spreading

Compartmentation of a building is designed to prevent
the spread of fire, smoke, and heat beyond a restricted area should a
fire break out. In a house, a fire-resistant plaster wall and a solid
wood door are required between an attached garage (where gasoline leaks
pose a potential fire hazard) and the dwelling. In rowhouses, fire-resistant
walls must be provided between dwellings (ill. 4 below).

In larger buildings, compartmentation becomes increasingly important,
both to protect the larger numbers of people inside and to prevent the unchecked spread of fire by hot
combustion gases. Stairways and corridors used as escape routes must
be isolated from the rest of the building by fire-resistant walls (usually
made of masonry, plaster, or concrete) and self-closing fire-resistant
doors (usually composed of steel facings with an incombustible mineral
core) (ill. 5 below). Fire-resistant walls and doors also are required
as separations between different types of functions taking place in the
same building. A boiler room, for example, must be separated in this
manner from the rest of a building so as to contain any fire that might
start there and prevent it from spreading. A woodworking shop or dry
cleaning establishment, either of which contains highly flammable substances,
must be separated from the remainder of a building that it shares with
other functions.

Open vertical shafts of any. kind, whether for stairs, elevators, ductwork,
electrical wiring, or piping, must be enclosed with
fire- resistant walls and self-closing fire-resistant
doors at each floor to prevent the convection of fire and combustion
products through the building (ill. 6 below). The only exceptions to
this rule are vertical atriums. Building codes define an atrium as a
roofed, inhabited, multistory open space contained within a building.
Atriums are commonly used in shopping arcades, hotels, and office buildings.
To avoid the spread of fire through these vertical spaces, designers
must comply with a number of building code provisions: The balconies
around an atrium may be open to it, but surrounding rooms must be isolated
from the balconies and atrium by fire-resistant walls. An exception is
made to this enclosure requirement for any three floors of the building
that the designer may choose, allowing lobby spaces on several floors
to be continuous with the atrium. The entire building that contains the
atrium and the atrium itself must be protected by sprinklers. and the
atrium must be provided with a system of fans that will operate automatically
in case of fire to bring fresh air into the space at ground level and exhaust smoke at the ceiling level.

Buildings with large floor areas must be subdivided into smaller areas
by means of fire-resistant walls and doors. In large,
single-story factories or warehouses where this is
not practical, incombustible curtain boards must be hung from the roof
to catch and contain the rising hot gases from a fire. A self-opening
roof vent must be provided in each compartment thus formed to allow the
hot gases to escape before they can spread the fire (ill. 7 below). The
roof vent doors are held closed against springs by a fusible link of
a special low-melting-point metal that releases them to open in case
of a buildup of heat.

In theaters, where the backstage area is often filled with combustible
scenery and temporary electrical wiring, the audience
must be protected by a fire-resistant curtain that
is normally rolled up above the proscenium. If a fire
breaks out, a fusible link melts and allows the curtain
to drop, sealing off the stage from the audience. A
large self-opening vent in the roof of the fly loft
above the stage relieves the heat and smoke in the backstage area (ill. 8 below).

Fire-resistant walls are required on the exteriors of many buildings.
The type of materials allowed in these walls and the
permissible extent and treatment of windows and doors
are governed by the proximity of each wall to the walls of neighboring
buildings. If two buildings are within a certain minimum distance, each
must have a parapet, a fire-resistant wall that projects a distance above
the roof in order to prevent fire from leaping from one roof to the next
(ill. .9 below).

The fire-resistive qualities of roof materials are also regulated by
law in urban areas to prevent easy ignition of a roof
by burning fragments thrown by a fire in an adjacent
building. Wired glass, which holds together against
flame for a considerable period of time, is usually
required in windows that face a nearby structure. Several
substitutes for wired glass have become available in
recent years, including a fire-resistant transparent ceramic that stays
intact at high temperatures. In multistory buildings, fire on a lower
floor can spread to upper floors by crawling up the face of the building
floor by floor, breaking windows and igniting combustible materials inside.
Two alternatives are open to the designer to solve this problem: a fire-resistant
spandrel at least 3 feet mm) high may be provided or else a horizontally
projecting flame barrier, also made of fire-resistant materials, at least
30 inches (762 mm) wide (ill. 10 below).